Surface electromyographic profiles during gait initiation in people with Parkinson's disease: The effects of external sensory cueing

Background Impaired gait initiation is a debilitating motor symptom in people with Parkinson's disease (PD). During self-paced (uncued) gait initiation, anticipatory postural adjustments (APAs) are often absent or attenuated, and the first steps are abnormally short. External sensory cues can significantly improve APAs. Objective The effect of external cueing on lower limb muscle activation during gait initiation, compared to self-initiated steps, was examined in people with PD and healthy older adults (HOA). Methods Ground reaction forces, center of pressure excursions, and lower-limb surface electromyographic profiles (in seven bilateral muscles) were examined in 32 individuals with PD (off-medication) and 10 age-matched HOA during the APA and first step of self-paced or acoustically cued gait initiation. Results Anterior (tibialis anterior, vastus lateralis, rectus femoris) and gluteus medius muscles were primarily activated during the early phases of gait initiation, while later phases predominantly involved posterior (soleus, gastrocnemius, biceps femoris) and gluteus medius activations. Cueing facilitated anterior muscles and suppressed posterior muscle activity in both groups, however, activation patterns in PD were not restored to HOA levels. Instead, the PD group had lower early activity during the APA (compared to HOA) and higher late activity. Conclusions Cueing increased anterior muscle activation during gait initiation, rather than evoking a global gain across muscles and timings, demonstrating that cueing predominantly facilitates neural circuitry critical for early APA phases. People with PD showed enhanced late phase activity, probably to compensate for ineffective APAs, and thus have a stronger need to facilitate cue-evoked improvements.